1. Field of the Invention
An object of the present invention is a device designed to be used in a microwave lens. It is designed, more particularly, to absorb the stray reflections that occur under high incidence.
2. Description of the Prior Art
An antenna, for example of the type described in the French patent No. 2.469.808, uses a microwave lens positioned in front of a source that gives it an electromagnetic wave. The lens described in the above patent is formed by a stack of phase-shifters separated by conductive planes, each phase-shifter being itself constituted by a stack of panels positioned along the direction of propagation of the wave. The wave emerging from the lens forms an angle .theta. with its initial direction. This angle .theta., called an angle of incidence, depends on the controls applied to the different phase-shifters.
When the angle of incidence is great, parasitic reflections of the microwave appear at the output face of the lens. This reflected wave, after going through the phase-shifters, returns towards the input face of of the lens, and at least a part of this energy gets reflected again. It again crosses the phase-shifters towards the output face where, at least in part, it comes out of the lens to form a parasitic radiation with an angle of incidence that is no longer the initial angle but is greater than it. Besides, that part of the energy which has not come out is again reflected, as described above, and gives rise to a new emerging parasitic beam, at an even greater angle of incidence, etc. When the radiation pattern of an antenna such as this is measured, secondary lobes due to the numerous reflections are thus seen to appear. This phenomenon grows in intensity with the value of the angle of incidence.